CBSE 2025 · Region 5 · Set 1 · Q38 · 4 marks
In human beings, there are $\displaystyle 23$ pairs of chromosomes. Out of these $\displaystyle 23$ pairs of chromosomes (i.e. $\displaystyle 46$ chromosomes), $\displaystyle 22$ pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types - 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl.(a)What are chromosomes ?(b)Why is the pair of sex chromosomes in human males called mismatched pair ?(c)Show with the help of a flow chart that the statistical probability of getting a boy or a girl is $\displaystyle 50$ : 50.(B)Mention two examples of animals where sex is not determined genetically like human beings. Describe in brief the method of sex determination in these animals.
In human beings, there are $\displaystyle 23$ pairs of chromosomes. Out of these $\displaystyle 23$ pairs of chromosomes (i.e. $\displaystyle 46$ chromosomes), $\displaystyle 22$ pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types - 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl.
(a)
What are chromosomes ?
(b)
Why is the pair of sex chromosomes in human males called mismatched pair ?
(c)
Show with the help of a flow chart that the statistical probability of getting a boy or a girl is $\displaystyle 50$ : 50.
(B)
Mention two examples of animals where sex is not determined genetically like human beings. Describe in brief the method of sex determination in these animals.
Marking-scheme solution
(a) Chromosomes carry genes which control the traits of an organism./Chromosomes contain information for inheritance of features from parents to next generation in form of DNA (deoxyribonucleic acid) molecules
(b) Men have one normal sized X chromosome while Y chromosome is short.
(c) (A)
OR
(B) • In a few reptiles; the temperature at which fertilized eggs are kept determine the sex of offspring.
In snails; the individual can change sex, indicating that is not genetically determined.
HereditySex DeterminationUnderstandcase_studymedium
More from Heredity
- Assertion: A mango seed will germinate to form a mango tree. Reason (R): Heredity determines the process by…2025 · asked 3×
- Assertion: In reptiles, the temperature at which the fertilized eggs are kept decides the sex of the…2025 · asked 3×
- A pure pea plant having round (R), yellow (Y) seeds is crossed with another pure pea plant having wrinkled…2025 · asked 3×
- "Proteins control the expression of various characters." Explain this statement by taking an example of…2025 · asked 3×
- Assertion: A human child bears all the basic features of human beings. Reason (R): It looks exactly like its…2025 · asked 3×
- If pea plants with round and green seeds (RRyy) are crossed with pea plants having wrinkled and yellow seeds…2025 · asked 3×
- When a pure-tall pea plant is crossed with a pure-dwarf pea plant, the percentage of tall pea plants in F 1…2025 · asked 3×
- The lowest part of the ear called earlobe, is closely attached to the side of the head in some of us (Figure…2025 · asked 2×
CBSE Class 10 Science past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.